From Proto-Indo-European to Proto-Germanic

Donald A. Ringe, From Proto-Indo-European to Proto-Germanic, A linguistic history of English, vol. 1 (Oxford: Oxford University Press, 2006).

This book is the first since 1897 to describe the earliest
reconstructable stages of the prehistory of English. It outlines the
grammar of Proto-Indo-European, considers the changes by which one
dialect of that prehistoric language developed into Proto-Germanic, and
provides a detailed account of the grammar of Proto-Germanic. The next
volume will consider the development of Proto-Germanic into Old English.